Microlayer membranes, improved battery separators, and methods of manufacture and use

ABSTRACT

In accordance with at least selected embodiments, a battery separator or separator membrane comprises one or more co-extruded multi-microlayer membranes optionally laminated or adhered to another polymer membrane. The separators described herein may provide improved strength, for example, improved puncture strength, particularly at a certain thickness, and may exhibit improved shutdown and/or a reduced propensity to split.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. provisionalpatent application Ser. No. 62/253,932 filed Nov. 11, 2015, hereby fullyincorporated by reference herein.

FIELD OF THE INVENTION

The disclosure or invention relates to novel or improved membranelayers, membranes or separator membranes, battery separators includingsuch membranes, and/or related methods. In accordance with at leastselected embodiments, the disclosure or invention relates to novel orimproved porous membranes or separator membranes, battery separatorsincluding such membranes, and/or related methods. In accordance with atleast certain embodiments, the disclosure or invention relates to novelor improved microporous membranes or separator membranes, microlayermembranes, multi-layer membranes including one or more microlayermembranes, battery separators including such membranes, and/or relatedmethods. In accordance with at least certain selected embodiments, thedisclosure or invention relates to novel, optimized or improvedmicroporous membranes or separator membranes having one or more novel orimproved exterior layers and/or interior layers, microlayer membranes,multi-layered microporous membranes or separator membranes havingexterior layers and interior layers, some of which layers are created byco-extrusion and all of which layers are laminated together to form thenovel, optimized or improved membranes or separator membranes. In someembodiments, certain layers comprise a homopolymer, a copolymer, and/ora polymer blend. The invention also relates to methods for making such amembrane, separator membrane, or separator, and/or methods for usingsuch a membrane, separator membrane or separator, for example as alithium battery separator. In accordance with at least selectedembodiments, the present application or invention is directed to novelor improved multi-layered and/or microlayer porous or microporousmembranes, separator membranes, separators, composites, electrochemicaldevices, batteries, methods of making such membranes, separators,composites, devices and/or batteries. In accordance with at leastcertain selected embodiments, the present invention is directed to anovel or improved separator membranes that are multi-layered, in whichone or more layers of the multi-layered structure is produced in amulti-layer or microlayer co-extrusion die with multiple extruders. Theimproved membranes, separator membranes, or separators may preferablydemonstrate improved shutdown, improved strength, improved dielectricbreakdown strength, and/or reduced tendency to split.

BACKGROUND OF THE INVENTION

Methods for reducing splitting in microporous battery separatormembranes, as well as particular split resistant or tear resistantmicroporous membranes, are discussed in U.S. Pat. No. 6,602,593. Suchpatent describes, among other things, a method that includes extruding afilm precursor by a blown film method and using a blow-up ratio (BUR) ofat least about 1.5 during blown film extrusion.

U.S. Pat. No. 8,795,565 describes, among other things, a biaxialstretching technique involving both MD and TD stretching of a dryprocess precursor membrane with a controlled MD relax process step.Biaxially stretched membranes, such as the membranes shown in FIGS. 1-3of the U.S. Pat. No. 8,795,565 patent, may have some reduced splittingor tearing. When a biaxially stretched microporous membrane is strengthtested using a puncture strength test method, the test sample puncturesite may be a round hole as opposed to an elongated split.

U.S. Pat. No. 8,486,556 discloses, among other things, a multi-layeredbattery separator membrane with increased strength. A high molecularweight polypropylene resin having a certain melt flow index was used toproduce multi-layered separators described in the U.S. Pat. No.8,486,556 patent.

Also described are wet process microporous battery separator membraneswhich are also typically uniaxially or biaxially stretched and which mayhave balanced MD and TD strength properties. Examples of microporousmembranes produced using a wet process may be disclosed in U.S. Pat.Nos. 6,666,969; 5,051,183; 6,096,213; and 6,153,133.

Various known methods of making microporous multi-layered membranes,such as for use as battery separator membranes, include laminating oradhering more than one monolayer precursor together or coextruding morethan one layer of membrane at the same time using a coextrusion die. Theaforementioned methods may not fully optimize a balance of strengthand/or performance properties for r use in applications such as certainprimary and/or secondary batteries, such as lithium ion rechargeablebatteries.

Hence, there is a need for a novel or improved co-extruded or laminated,multi-layered microporous membrane, base film, or battery separatorhaving various improvements, such as improved tensile strength andimproved dielectric breakdown strength.

SUMMARY OF THE INVENTION

In accordance with at least selected embodiments, the presentapplication or invention may address the above needs or issues, mayaddress the need for a novel or improved co-extruded or laminated,multi-layered porous, macroporous, mesoporous, microporous, ornanoporous membrane, base film, or battery separator having variousimprovements, such as improved tensile strength and improved dielectricbreakdown strength, and/or may provide novel or improved co-extrudedand/or laminated, multi-layered and/or multi-microlayered (ormulti-nanolayered) microporous membranes, base films, or batteryseparators possibly preferably having various improvements, such asimproved shutdown, mechanical strength, porosity, permeability,splittiness (reduced splitting), tensile strength, oxidation resistance,adhesion, wettability, and/or dielectric breakdown strength, and/ornovel or improved membrane layers, membranes or separator membranes,battery separators including such membranes, and/or related methods. Inaccordance with at least selected embodiments, the disclosure orinvention relates to novel or improved porous membranes or separatormembranes, battery separators including such membranes, and/or relatedmethods. In accordance with at least certain embodiments, the disclosureor invention relates to novel or improved microporous membranes orseparator membranes, microlayer membranes, multi-layer membranesincluding one or more microlayer membranes, battery separators includingsuch membranes, and/or related methods. In accordance with at leastcertain selected embodiments, the disclosure or invention relates tonovel, optimized or improved microporous membranes or separatormembranes having one or more novel or improved exterior layers and/orinterior layers, microlayer membranes, multi-layered microporousmembranes or separator membranes having exterior layers and interiorlayers, some of which layers are created by co-extrusion and all ofwhich layers are laminated together to form the novel, optimized orimproved membranes or separator membranes. In some embodiments, certainlayers comprise a homopolymer, a copolymer, and/or a polymer blend. Theinvention also relates to methods for making such a membrane, separatormembrane, or separator, and/or methods for using such a membrane,separator membrane or separator, for example as a lithium batteryseparator. In accordance with at least selected embodiments, the presentapplication or invention is directed to novel or improved multi-layeredand/or microlayer porous or microporous membranes, separator membranes,separators, composites, electrochemical devices, batteries, methods ofmaking such membranes, separators, composites, devices and/or batteries.In accordance with at least certain selected embodiments, the presentinvention is directed to a novel or improved separator membranes thatare multi-layered, in which one or more layers of the multi-layeredstructure is produced in a multi-layer or microlayer co-extrusion diewith one or more extruders feeding the die (typically one extruder perlayer or microlayer). The improved membranes, separator membranes,and/or separators may preferably demonstrate improved shutdown, improvedstrength, improved dielectric breakdown strength, and/or reducedtendency to split.

In accordance with at least certain embodiments, the present applicationor invention may address the above needs or issues and/or may providenovel or improved porous membranes or substrates, separator membranes,separators, composites, electrochemical devices, batteries, methods ofmaking such membranes or substrates, separators, and/or batteries,and/or methods of using such membranes or substrates, separators and/orbatteries. In accordance with at least certain embodiments the instantbattery separator may comprise one or more co-extruded multi-layermembranes of like and/or distinct polymers or co-polymers laminated oradhered to another membrane. For instance, and not meant to be limiting,in certain embodiments, an inventive battery separator may comprise atleast two co-extruded multi-layer membranes of like and/or distinctpolymers or co-polymers that are laminated or adhered to each other orto another polymer membrane (monolayer or multi-layer membrane of likeand/or distinct polymers or co-polymers). For example, a batteryseparator in one embodiment may comprise, but is not limited to, apolyethylene/polyethylene/polyethylene (PE/PE/PE) coextruded trilayermembrane laminated to a polypropylene (PP) monolayer and, in someembodiments, further laminated to another PE/PE/PE coextruded trilayermembrane to form the following constructions, [PE/PE/PE]/PP/[PE/PE/PE]or [PE/PE/PE]/PP or PP/[PE/PE/PE]/PP or [PE/PE/PE]/PP/PP or[PE/PE/PE]/[PE/PE/PE]/PP or other multi-layer constructions, where eachof the individual co-extruded polymer layers are preferably micrometeror nanometer in thickness (microlayers or nanolayers). In otherembodiments, a PE/PE/PE coextruded trilayer membrane may be laminated toa coextruded PP/PP/PP trilayer membrane, and in some embodiments,further laminated to another PE/PE/PE or PP/PP/PP coextruded trilayermembrane to form the following constructions,[PE/PE/PE]/[PP/PP/PP]/[PE/PE/PE] or [PP/PP/PP]/[PE/PE/PE]/[PP/PP/PP] or[PE/PE/PE]/[PP/PP/PP] or [PE/PE/PE]/[PE/PE/PE]/[PP/PP/PP] or[PE/PE/PE]/[PP/PP/PP]/[PP/PP/PP] or other multi-layer constructions,where each of the individual co-extruded polymer layers are preferablymicrometer or nanometer in thickness (microlayers or nanolayers). Instill other embodiments, a PP/PE/PP or PP/PP/PP or PE/PE/PE or PE/PP/PEor PP/PP/PE or PE/PE/PP coextruded trilayer membrane may be laminated toa coextruded PP/PP/PP or PE/PE/PE or PP/PE/PP or PE/PP/PE or PP/PP/PE orPE/PE/PP trilayer membrane, and in some embodiments, further laminatedto another PP/PP/PP or PE/PE/PE or PP/PE/PP or PE/PP/PE or PP/PP/PE orPE/PE/PP coextruded trilayer membrane to form the followingconstructions, [PP/PE/PP]/[PP/PP/PP]/[PE/PE/PE] or[PP/PE/PP]/[PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PE/PE/PE]/[PP/PP/PP] or[PP/PE/PP]/[PP/PE/PP]/[PP/PE/PP] or [PE/PE/PE]/[PE/PE/PE]/[PE/PE/PE] or[PE/PE/PE]/[PE/PE/PE] or [PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PP/PP/PP]or [PP/PP/PP]/[PP/PP/PP]/[PP/PP/PP] or [PE/PE/PE]/[PE/PE/PE]/[PP/PP/PP]or [PP/PP/PP]/[PP/PP/PP]/[PE/PE/PE] or [PE/PE/PP]/[PP/PP/PP] or[PP/PP/PP]/[PP/PP/PE] or [PE/PP/PP]/[PP/PP/PP]/[PP/PP/PE] or[PE/PE/PP]/[PP/PE/PE] or [PP/PP/PP]/[PP/PP/PP]/[PP/PE/PE] or othercombinations or multi-layer constructions, where each of the individualco-extruded polymer layers are preferably micrometer or nanometer inthickness (microlayers or nanolayers). In yet still other embodiments, aPP/PE/PP or PP/PP/PP or PE/PE/PE or PE/PP/PE or PE/PP/PP or PE/PE/PP orPP+PE/PP/PP or PP+PE/PP/PP+PE or PP+PE/PP+PE/PP+PE or PP+PE/PE/PE orPP+PE/PP/PE or PP+PE/PE/PP or other coextruded trilayer membranes of PP,PE or PP+PE may be laminated to a coextruded PP/PE/PP or PP/PP/PP orPE/PE/PE or PE/PP/PE or PE/PP/PP or PE/PE/PP or PP+PE/PP/PP orPP+PE/PP/PP+PE or PP+PE/PP+PE/PP+PE or PP+PE/PE/PE or PP+PE/PP/PE orPP+PE/PE/PP or other trilayer membranes of PP, PE, or PP+PE, and in someembodiments, further laminated to another PP/PE/PP or PP/PP/PP orPE/PE/PE or PE/PP/PE or PE/PP/PP or PE/PE/PP or PP+PE/PP/PP orPP+PE/PP/PP+PE or PP+PE/PP+PE/PP+PE or PP+PE/PE/PE or PP+PE/PP/PE orPP+PE/PE/PP or other coextruded trilayer membranes of PP, PE, or PP+PEto form the following constructions, [PP/PE/PP]/[PP/PP/PP] or[PP/PE/PP]/[PE/PE/PE] or [PP/PP/PP]/[PE/PE/PE] or [PP/PE/PP]/[PP/PE/PP]or [PE/PE/PE]/[PE/PE/PE] or [PE/PE/PE]/[PP/PP/PP] or[PP/PP/PP]/[PP/PP/PP] or [PP/PP/PP]/[PP/PP/PP]/[PP/PP/PP] or[PE/PE/PE]/[PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PP/PP/PP]/[PE/PE/PE] or[PP/PE/PE]/[PE/PE/PE] or [PP/PP/PE]/[PE/PE/PE] or [PE/PP/PP]/[PP/PP/PE]or [PP+PE/PP/PP]/[PP/PP/PP+PE] or [PP/PE/PP]/[PP/PP/PP]/[PE/PE/PE] or[PP/PE/PP]/[PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PE/PE/PE]/[PP/PP/PP] or[PP/PE/PP]/[PP/PE/PP]/[PP/PE/PP] or [PE/PE/PE]/[PE/PE/PE]/[PE/PE/PE] or[PE/PE/PE]/[PE/PE/PE] or [PP/PP/PP]/[PP/PP/PP]/[PP/PP/PP] or[PE/PE/PE]/[PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PP/PP/PP]/[PE/PE/PE] or[PP/PE/PE]/[PE/PE/PEMPE/PE/PP] [PP/PP/PE]/[PE/PE/PE]/[PE/PP/PP] or[PE/PP/PP]/[PP/PP/PP]/[PP/PP/PE] or [PP+PE/PP/PP]/[PP/PP/PPMPP/PP/PP+PE]or [PP/PE/PP]/[PP/PE/PE] or [PE/PP/PE]/[PE/PP/PP] or[PE/PE/PP]/[PP/PE/PE] or [PP+PE/PP/PP]/[PP/PP/PP+PE] or[PP+PE/PP/PP+PE]/[PP+PE/PP+PE/PP+PE] or [PP+PE/PE/PE]/[PP+PE/PP/PE] or[PP+PE/PE/PE]/[PP+PE/PP/PE]/[PP+PE/PE/PP] or other combinations orsubcombinations of PP, PE, or PP+PE layers (blends, mixtures, orco-polymers), microlayers, nanolayers, or combinations thereof, or othermulti-layer constructions, where each of the individual co-extrudedpolymer layers are preferably micrometer or nanometer in thickness(microlayers or nanolayers).

Although certain multi-layer polymer membrane embodiments (bi-layer,tri-layer, quad-layer, penta-layer, . . . ) may be preferred (and thatone or more layers, treatments, materials, or coatings (CT) and/or nets,meshes, mats, wovens, or non-wovens (NW) may be added on one or bothsides, or within the multilayer membrane (M) which may include one ormore co-extruded layers or sub-layers (CX), such as, but not limited to,CT/M, NW/M, CT/M/CX, CT1/M/CT2, CT/CX1/CX2/NW, CT1/CX1/CX2/CX3/CT2,CT/CX1/CX2, NW/CX1/CX2, NW1/CX1/CX2/CX3/NW2, CT/NW/CX1/CX2, CX1/NW/CX2,CX1/CT/CX2, and or combinations or subcombinations of M, CX, CT, and/orNW), it is also contemplated that single layer or mono-layer ormulti-layer membranes (M) or embodiments made up of one or moremicrolayers or nanolayers of PP, PE, or PE+PP (preferably more than one)(and that one or more coatings (CT) and/or non-wovens (NW) may be addedon one or both sides of the membrane (M or CX), such as, but not limitedto, CT/M, NW/M, CT/M/CX, CT/CX/NW, CT1/CX/CT2, NX1/CX/NW2, CT/CX/NW/CT,NW1/CX/NW2/CT, CT1/NW/CX/CT2, and or combinations or subcombinations ofM, CX, CT, and/or NW) and may include constructions PP or PE or PE+PP orPP/PE or PP/PP or PE/PE or PP+PE/PP or PP+PE/PP+PE or PP+PE/PE orPP/PE/PP or PP/PP/PP or PE/PE/PE or PE/PP/PE or PE/PP/PP or PE/PE/PP orPP+PE/PP/PP or PP+PE/PP/PP+PE or PP+PE/PP+PE/PP+PE or PP+PE/PE/PE orPP+PE/PP/PE or PP+PE/PE/PP coextruded membranes which may be laminatedto one or more other membranes (extruded or coextruded) PP or PE orPE+PP or PP/PE or PP/PP or PE/PE or PP+PE/PP or PP+PE/PP+PE or PP+PE/PEor PP/PE/PP or PP/PP/PP or PE/PE/PE or PE/PP/PE or PE/PP/PP or PE/PE/PPor PP+PE/PP/PP or PP+PE/PP/PP+PE or PP+PE/PP+PE/PP+PE or PP+PE/PE/PE orPP+PE/PP/PE or PP+PE/PE/PP membranes, and in some embodiments, furtherlaminated to another PP or PE or PE+PP or PP/PE or PP/PP or PE/PE orPP+PE/PP or PP+PE/PP+PE or PP+PE/PE or PP/PE/PP or PP/PP/PP or PE/PE/PEor PE/PP/PE or PE/PP/PP or PE/PE/PP or PP+PE/PP/PP or PP+PE/PP/PP+PE orPP+PE/PP+PE/PP+PE or PP+PE/PE/PE or PP+PE/PP/PE or PP+PE/PE/PP membraneor membranes to form the following constructions, PP or PE or PE+PP orPP/PE or PP/PP or PE/PE or PP+PE/PP or PP+PE/PP+PE or PP+PE/PE or[PP/PE/PP]/[PP/PP/PP] or [PP/PE/PP]/[PE/PE/PE] or [PP/PP/PP]/[PE/PE/PE]or [PP/PE/PP]/[PP/PE/PP] or [PE/PE/PE]/[PE/PE/PE] or[PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PP/PP/PP] or[PP/PP/PP]/[PP/PP/PP]/[PP/PP/PP] or [PE/PE/PE]/[PE/PE/PE]/[PP/PP/PP] or[PP/PP/PP]/[PP/PP/PP]/[PE/PE/PE] or [PP/PE/PE]/[PE/PE/PE] or[PP/PP/PE]/[PE/PE/PE] or [PE/PP/PP]/[PP/PP/PE] or[PP+PE/PP/PP]/[PP/PP/PP+PE] or [PP/PE/PP]/[PP/PP/PP]/[PE/PE/PE] or[PP/PE/PP]/[PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PE/PE/PE]/[PP/PP/PP] or[PP/PE/PP]/[PP/PE/PP]/[PP/PE/PP] or [PE/PE/PE]/[PE/PE/PE]/[PE/PE/PE] or[PE/PE/PE]/[PE/PE/PE] or [PP/PP/PP]/[PP/PP/PP]/[PP/PP/PP] or[PE/PE/PE]/[PE/PE/PE]/[PP/PP/PP] or [PP/PP/PP]/[PP/PP/PP]/[PE/PE/PE] or[PP/PE/PE]/[PE/PE/PE]/[PE/PE/PP] [PP/PP/PE]/[PE/PE/PE]/[PE/PP/PP] or[PE/PP/PP]/[PP/PP/PP]/[PP/PP/PE] or[PP+PE/PP/PP]/[PP/PP/PP]/[PP/PP/PP+PE] or [PP/PE/PP]/[PP/PE/PE] or[PE/PP/PE]/[PE/PP/PP] or [PE/PE/PP]/[PP/PE/PE] or[PP+PE/PP/PP]/[PP/PP/PP+PE] or [PP+PE/PP/PP+PE]/[PP+PE/PP+PE/PP+PE] or[PP+PE/PE/PE]/[PP+PE/PP/PE] or [PP+PE/PE/PE]/[PP+PE/PP/PE]/[PP+PE/PE/PP]or other such combinations or subcombinations of PP, PE, or PP+PE(blends, mixtures, or co-polymers) layers, microlayers, nanolayers, orcombinations thereof, or other multi-layer constructions, where each ofthe individual co-extruded polymer layers are preferably micrometer ornanometer in thickness (microlayers or nanolayers).

Although it may be preferred that each of the layers or microlayers ornanolayers be polyolefin (PO) such as PP or PE or PE+PP blends,mixtures, co-polymers, or the like, it is contemplated that otherpolymers (PY), additives, agents, materials, fillers, and/or particles(M), and/or the like may be added or used and may form layers,microlayers, nanolayers, or membranes such as PP+PY, PE+PY, PP+M, PE+M,PP+PE+PY, PE+PP+M, PP+PY+M, PE+PY+M, PP+PE+PY+M, or blends, mixtures,co-polymers, and/or the like thereof, and that such layers or membranesmay be used in combination with one or more PP or PE or PE+PP layers ormembranes.

Also, identical, similar, distinct, or different PP or PE or PE+PPpolymers, homopolymers, copolymers, molecular weights, blends, mixtures,co-polymers, or the like layers, microlayers, nanolayers, or membranes,may be used in many different combinations and subcombinations to formlayers, sub-layers, membranes, or sub-membranes. For example, identical,similar, distinct, or different molecular weight PP, PE, and/or PP+PEpolymers, homopolymers, co-polymers, multi-polymers, blends, mixtures,and/or the like may be used in each layer or membrane or in eachindividual layer, microlayer, nanolayer, or membrane. As such,constructions may include various combinations and subcombinations ofPP, PE, PP+PE, PP1, PP2, PP3, PE1, PE2, PE3, PP1+PP2, PE1+PE2,PP1+PP2+PP3, PE1+PE2+PE3, PP1+PP2+PE, PP+PE1+PE2, PP1/PP2, PP1/PP2/PP1,PE1/PE2, PE1/PE2/PP1, PE1/PE2/PE3, PP1+PE/PP2, or other combinations orconstructions. For example, inventive membrane or separator propertiescan be improved, modified or optimized by, for example, adjusting theouter layer or membrane surface by using a particular polymer, blend,molecular weight polymer, and/or the like in just the outer layer ormembrane surface. As a non-limiting example, an outer PE or PP+PEsurface or layer may have improved pin removal (lower COF), a highermolecular weight (MW) polymer surface or layer (PP or PE) may haveimproved puncture strength, a PP or PP+PE surface or layer may haveimproved oxidation resistance, expensive raw materials (expensivepolymers) can be used in limited layers to reduce cost, and/or the like.Further, although it may be preferred that each of the layers ormicrolayers or nanolayers be polyolefin (PO) such as PP or PE or PE+PPblends, mixtures, co-polymers, or the like, it is contemplated thatother polymers (PY), additives, agents, materials, fillers, and/orparticles (M), and/or the like may be added or used and may form layers,microlayers, nanolayers, or membranes such as different outer or surfacelayers that may be used in combination with one or more PP or PE orPE+PP layers or membranes, and that coatings (CT) or nonwovens (NW) maybe added.

The production of monolayer or multi-layer porous, microporous ornanoporous membranes according to various inventive embodiments herein,may allow for improved characteristics such as improved shutdown,mechanical strength, porosity, permeability, oxidation resistance, pinremoval, wettability, and/or splittiness (reduced splitting), and thelike.

In one embodiment of the invention, a multi-layer membrane may beextruded in the form of a PE homopolymer/PE homopolymer, or PPhomopolymer/PP homopolymer, or one or more layers of such a multi-layermembrane may include a blend of two polymers, such as a blend ofPEs/homopolymer PE, and so forth.

The microlayer membrane precursors may be bonded together via laminationor adhesion. The possibly preferred battery separators described hereinmay exhibit a total thickness of less than about 30 μm, less than about25 μm, less than about 20 μm, less than about 16 μm, less than about 15μm, less than about 14 μm, or less than about 10 μm, less than about 9μm, less than about 8 μm, or less than about 6 μm (depending on thenumber of layers) and may surprisingly exhibit increased strengthperformance, as defined by reduced splittiness or reduced propensity tosplit, when compared to known battery separators of the same (orgreater) thickness, especially when compared to known dry processbattery separators of the same (or greater) thickness. The improvementin splitting or splittiness may be quantified by a test method disclosedherein as Composite Splittiness Index (CSI) and the novel or improvedseparators described herein may have an improvement in the CSI, and alsomay exhibit improved Gurley as well as other improvements, such asimproved puncture strength and so forth.

In at least one embodiment the inventive membrane may be constructed ofmany microlayers or nanolayers wherein the final product may contain 50or more layers of individual microlayers or nanolayers. In at leastcertain embodiments the microlayer or nanolayer technology may becreated by in a pre-encapsulation feedblock prior to entering a castfilm or blown film die.

In at least selected embodiments the microlayer or nanolayer membranemay contain 3 or more layers of individual coextruded microlayers ornanolayers and may have improved strength, improved cycling, greatertortuosity, and favorable compression resistance and/or recovery.

In at least selected embodiments the microlayer or nanolayer membranemay contain 3 or more layers of individual coextruded microlayers ornanolayers and may have improved strength, improved cycling, greatertortuosity, and/or favorable compression resistance and/or recovery.

In at least selected embodiments the microlayer or nanolayer membranemay contain 9 or more layers of individual coextruded microlayers ornanolayers and may have improved strength, improved cycling, greatertortuosity, and/or favorable compression resistance and/or recovery.

In at least selected embodiments the microlayer or nanolayer membranemay contain 5 or more layers of individual coextruded microlayers ornanolayers and may have improved strength, improved cycling, greatertortuosity, and/or favorable compression resistance and/or recovery.

In at least certain selected embodiments the microlayer membrane maycontain 3 or more layers of individual coextruded microlayers and mayhave improved strength, improved cycling, greater tortuosity, and/orfavorable compression resistance and/or recovery.

In at least certain selected particular embodiments the multi-layermembrane may contain 2 or more layers of individual coextrudedmicrolayers that are laminated together and may have improved strength,improved cycling, greater tortuosity, and/or favorable compressionresistance and/or recovery.

In at least certain selected particular embodiments the multi-layermembrane may contain 3 or more layers of individual coextrudedmicrolayers that are laminated together and may have improved strength,improved cycling, greater tortuosity, and/or favorable compressionresistance and/or recovery.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a partial cross-section Scanning Electron Micrograph (SEM) ofan exemplary inventive laminated 3 layer or triple trilayer microporousmembrane trilayer/trilayer/trilayer (with 9 coextruded microlayers pereach trilayer layer, and with 3 microlayers per each PP or PE sub-layerof each trilayer layer) at a magnification of 2,500× (at least the outerPP layers of each layer are microporous).

FIG. 2 is a partial cross-section Scanning Electron Micrograph (SEM) ofa portion of the polypropylene surface sub-layer (3 microlayers of PP)of the surface trilayer component or sub-membrane of the compositelaminated membrane of FIG. 1 at a magnification of 15,000× (the PP.

FIG. 3 is a partial cross-section Scanning Electron Micrograph (SEM) ofthe polyethylene sub-layer (3 microlayers of PE) of one of the 9microlayer trilayer layers of the 3 layer membrane of FIG. 1 at amagnification of 15,000×.

FIG. 4 is a graph demonstrating the improved cycling behavior ofexemplary inventive constructions as compared to EH1211.

FIG. 5 is a graph demonstrating compression elasticity results ofcertain constructions as compared to EH1211.

FIG. 6 is a graph demonstrating Mix P penetration test results ofcertain constructions as compared to EH1211.

FIG. 7 is a schematic diagram of how microlayers may be created in thefeedblock by layer multiplication.

FIG. 8 is a schematic diagram of how microlayers may be created by layersplitting.

FIG. 9 is a cross-section Scanning Electron Micrograph (SEM) of anexemplary inventive 3 layer or trilayer (9 microlayers total, with 3triple microlayer sub-layers laminated together) PP/PE/PP microporousmembrane at a magnification of 5,000× (at least the outer PP sub-layersare microporous).

FIG. 10 is a surface Scanning Electron Micrograph (SEM) of a surface ofthe polypropylene surface sub-layer (surface PP microlayer) of the 9microlayer, 3 layer membrane of FIG. 9 at a magnification of 3,000×.This 9 microlayer membrane could be used as one layer of a 3 layermembrane such as shown in FIG. 1.

FIG. 11 is a surface Scanning Electron Micrograph (SEM) of a portion ofthe surface of the polypropylene surface sub-layer (surface PPmicrolayer) of the 9 microlayer layer, 3 layer membrane of FIG. 9 at amagnification of 10,000×.

FIG. 12 is a surface Scanning Electron Micrograph (SEM) of a portion ofthe surface of the polypropylene surface sub-layer (surface PPmicrolayer) of the 9 microlayer, 3 layer membrane of FIG. 9 at amagnification of 30,000×.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with at least selected embodiments, aspects or objects,the present application or invention may address the above needs orissues, and/or may provide novel or improved membrane layers, porousmembranes or substrates, separator membranes, separators, composites,electrochemical devices, batteries, methods of making such membranes orsubstrates, separators, and/or batteries, and/or methods of using suchmembranes or substrates, separators and/or batteries. In accordance withat least certain embodiments the instant battery separator comprises aone or more co-extruded micro-layer or microlayer membranes laminated oradhered to another polymer membrane. For example, in some instances, thebattery separator may comprise, but is not limited to, apolyethylene/polyethylene/polyethylene (PE/PE/PE) coextrudedmicro-trilayer membrane laminated to a polypropylene (PP) monolayermicro or nanolayer membrane, and, in some embodiments, further laminatedto another PE/PE/PE coextruded micro-trilayer membrane, to form thefollowing construction: [PE/PE/PE]/PP/[PE/PE/PE]. In selectedembodiments, the membrane, membrane precursor, sub-membrane, layer, orsub-layer may be comprised of one or more microlayers. A microlayer isdefined herein as a layer or individual layer, for example, of polymeror co-polymer blend, that is preferably less than about 5 μm thick, morepreferably less than about 4 μm, still more preferably less than about 3μm, and possibly most preferably less than about 2 μm. In selectedembodiments, the membrane, membrane precursor, sub-membrane, layer, orsub-layer may be comprised of one or more nanolayers. A nanolayer isdefined herein as a layer or individual layer, for example, of polymeror co-polymer blend, that is less than about 1 μm thick, more preferablyless than about 0.5 μm, still more preferably less than about 0.3 μm,and possibly most preferably less than about 0.2 μm.

A novel microporous battery separator has been developed for use in alithium ion rechargeable battery. The possibly preferred inventiveseparator membrane, separator, base film, or membrane may, in someembodiments, comprise a polyethylene/polyethylene/polyethylene(PE/PE/PE) coextruded microlayer (PE micro-trilayer) membrane laminatedto another membrane, such as a polypropylene (PP) monolayer membrane,and in some instances, further laminated to another PE/PE/PE coextrudedmicrolayer membrane to form the following construction:[PE/PE/PE]/PP/[PE/PE/PE]. Possibly preferred separator, membrane or basefilm thickness may range from 5 um to 30 um. FIG. 1 demonstrates the 9microlayer coextruded construction of each of the 3 layers of themembrane (the 3 layers are laminated together to form the membrane). Ineach of the polymer sub-layers of the 9 microlayer layers, there arethree microlayers that create the PP or PE sub-layer. FIGS. 2 and 3 showmagnified views of the three microlayers highlighting the continuitybetween each of the microlayers of each layer. FIG. 3 shows thecontinuity between the polypropylene and polyethylene microlayers. Themicrolayers of at least each 9 microlayer coextruded layer in FIGS. 1-3have undefined adjacent microlayer interfaces, this seamless interfacingbetween microlayers may contribute to improved cycling, increasedsurface area, and higher tortuosity.

EXAMPLES

In the Examples, various membranes were made having the construction of[PE/PE/PE]/PP/[PE/PE/PE]. Their characteristics are shown in Table 1,just below:

The various membranes Ex 1, Ex 2, and Ex 3 made as inventive Examplesdemonstrate (as shown in Table 1 below) improved puncture strength andan improvement in dielectric breakdown (DB) over the control CE 1.

TABLE 1 Example Number CE 1 Ex 1 Ex 2 Ex 3 Thickness (microns) 14 1414.4 14.5 JIS Gurley (seconds) 220 291 306 309 Puncture Strength 265 323294 291 Average (g) MD Tensile Stress 2500 2867 2668 2802 (kgf/cm²) TDTensile Stress 125 118 132 128 (kgf/cm²) TD elongation average 980 978751 854 (%) Shrinkage at 105° C. (%) 1.7 2.5 4.4 4.2 Calculated Porosity 40%  42%  40%  37% Outside Layer/Middle 0.054/ 0.045/ 0.041/ 0.042/layer Pore size 0.028 0.028 0.027 .027 MixP (Relative −46% −52% −47%−48% to control) Dielectric Breakdown 1510 1720 1835 1649 Average(volts)

In accordance with at least certain embodiments, the present inventionis directed to a multi-layered battery separator or separator membranewhose exterior surface comprises multiple layers that in some instanceshave been co-extruded, for example, a co-extruded multi-layer membraneof polyethylene (PE) homopolymer, which is adhered or laminated to apolypropylene monolayer and an additional multi-layered coextrudedmulti-layer membrane comprising polyethylene homopolymer.

In accordance with at least certain embodiments, the present inventionis directed to a multi-layered battery separator or separator membranewhose exterior surface

Also, performance can be further improved, optimized, selected,controlled, or the like.

In accordance with at least certain embodiments, the present inventionis directed to a multi-layered battery separator or separator membranewhose exterior surface comprises multiple layers that in some instanceshave been co-extruded, for example, a co-extruded multi-layer membraneof polyethylene (PE) homopolymer, which is adhered or laminated to apolypropylene monolayer and an additional multi-layered coextrudedmulti-layer membrane comprising polyethylene homopolymer.

In accordance with at least certain embodiments, the present inventionis directed to a multi-layered battery separator or separator membranewhose exterior surface comprises multiple layers and one or more ofwhich layers includes a polyethylene (PE) blend and/or a PE copolymer,which is adhered or laminated to a polypropylene monolayer and anadditional multi-layered coextruded multi-layer membrane, one or more ofwhich layers includes a polyethylene blend and/or a PE copolymer.

In accordance with at least certain embodiments, the present inventionis directed to a multi-layered battery separator or separator membranewhose exterior surface comprises multiple layers and one or more layersof which includes a polyethylene (PE) homopolymer while one or morelayers of which includes a polyethylene blend and/or a PE copolymer,which is adhered or laminated to a polypropylene monolayer and anadditional multi-layered coextruded membrane, one or more layers ofwhich includes a polyethylene (PE) homopolymer while one or more layersof which includes a polyethylene blend and/or a copolymer blend. Otherpossibilities for such constructions are also included in this inventionin which at least one co-extruded multi-layer membrane is laminated toat least one other membrane to form a multi-layer construction thatcombines aspects of co-extruded membranes with aspects of laminatedmembranes.

Multi-layered polyolefin membranes are designed to provide an exteriorsurface that has a low pin removal force, faster wetting, good coatingadhesion, tunable shutdown and the like. Each layer of polymer islaminated or co-extruded with the resulting membrane having significantimprovements in many characteristics. The invention herein describedutilizes both the co-extrusion and lamination of one or more multi-layermembranes to improve surface characteristics. In accordance with atleast certain embodiments the present invention may provide an exteriorsurface that has improved shutdown function, improved longitudinalstrength, and an increase in dielectric breakdown.

The polymers or co-polymers that may be used in the instant batteryseparator are those that are extrudable. Such polymers are typicallyreferred to as thermoplastic polymers. Exemplary thermoplastic polymers,blends, mixtures or copolymers may include, but are not limited to:polyolefins, polyacetals (or polyoxymethylenes), polyamides, polyesters,polysulfides, polyvinyl alcohols, polyvinyl esters, and polyvinylidenes(and may include PVDF, PVDF:HFP, PTFE, PEO, PVA, PAN, or the like).Polyolefins include, but are not limited to: polyethylene (including,for example, LDPE, LLDPE, HDPE, UHDPE, UHMWPE, and so forth),polypropylene, polybutylene, polymethylpentene, copolymers thereof, andblends thereof. Polyamides (nylons) include, but are not limited to:polyamide 6, polyamide 66, Nylon 10, 10, polyphthalamide (PPA),co-polymers thereof, and blends thereof. Polyesters include, but are notlimited to: polyester terephthalate, polybutyl terephthalate, copolymersthereof, and blends thereof. Polysulfides include, but are not limitedto, polyphenyl sulfide, copolymers thereof, and blends thereof.Polyvinyl alcohols include, but are not limited to: ethylene-vinylalcohol, copolymers thereof, and blends thereof. Polyvinyl estersinclude, but are not limited to, polyvinyl acetate, ethylene vinylacetate, copolymers thereof, and blends thereof. Polyvinylidenesinclude, but are not limited to: fluorinated polyvinylidenes (e.g.,polyvinylidene chloride, polyvinylidene fluoride), copolymers thereof,and blends thereof. Various materials may be added to the polymers.These materials are added to modify or enhance the performance orproperties of an individual layer or the overall separator. Suchmaterials include, but are not limited to: Materials to lower themelting temperature of the polymer may be added. Typically, themulti-layered separator includes a layer designed to close its pores ata predetermined temperature to block the flow of ions between theelectrodes of the battery. This function is commonly referred to asshutdown.

FIG. 4 shows the cycling performance of the microlayer membranes ascompared to EH1211. In each sample, the microlayer construction showedmaintained or improved cycling performance.

In at least selected embodiments, the microlayers or nanolayers mayinclude various additives in one or more layers for example, to reducepin removal force while not affecting the adhesion between PP and PE in,for example, micro-trilayer applications. In certain instances theadditives may be applied to the outside microlayers. The outermicrolayers may comprise or consist of PP with Siloxaneadditives/homopolymer PP/homopolymer PP. The additives can include allthat could affect the surface characteristics of the film, some examplesinclude: PE, Calcium Stearate, Lithium Stearate, and/or Siloxane.

In accordance with at least selected embodiments, aspects or objects,the present application or invention may be directed to: a batteryseparator or separator membrane that comprises one or more co-extrudedmulti-layer membranes laminated or adhered to another polymer membraneand/or to another co-extruded multi-layer membrane, and/or suchseparators that may provide improved strength, for example, improvedpuncture strength, particularly at a certain thickness, and/or mayexhibit improved shutdown and/or a reduced propensity to split.

In accordance with at least certain embodiments, aspects or objects, thepresent application or invention may be directed to: a battery separatoror separator membrane that comprises one or more co-extruded multi-layermicrolayer and/or nanolayer membranes, and/or such separators that mayprovide improved strength, for example, improved puncture strength,particularly at a certain thickness, and/or may exhibit improvedshutdown and/or a reduced propensity to split.

In accordance with at least certain embodiments, aspects or objects, thepresent application or invention may be directed to: a battery separatoror separator membrane that comprises one or more co-extruded multi-layermicrolayer and/or nanolayer membranes co-extruded, laminated or adheredto another polymer membrane and/or to another co-extruded multi-layermembrane, and/or such separators that may provide improved strength, forexample, improved puncture strength, particularly at a certainthickness, and/or may exhibit improved shutdown and/or a reducedpropensity to split.

Table 2 shows a comparison of the 9 microlayer, 12 μm, membrane with amore conventional structure 12 μm trialyer membrane (EH1211). Whencompared to the conventional trilayer, the inventive microlayer 12 μmmembrane exhibited increased mechanical strength and a significantreduction in shrinkage. FIG. 6 shows Mix P or mix penetration testresults for the 9 microlayer 12 μm microporous membrane. The inventivemicrolayer membrane exhibited the greatest resistance to penetration at650 N force.

TABLE 2 Product EH1211 9-microlayer construction Thickness (um) 12 12JIS Gurley 225 234 Puncture Strength Average 277 318 MD Tensile Stress(kgf/cm²⁾ 2231 2393 TD Tensile Stress (kgf/cm²⁾ 138 139 MD elongation(%) 48 51 TD elongation (%) 704 756 QC Porosity 42% — MD Shrinkage @105° C. (%) 3.7 1.0Table 3 shows comparison of the 9 microlayer 12 μm membrane (R0384) to amore conventional 12 μm dry process membrane (EH1211). The microlayerconstruction provides greater compression recovery than the comparablewet process membrane. In certain applications, less crush and/or bettercompression recovery may be desired.

TABLE 3 Sample EH1211 R0384 Thickness (μm) 12 12 Mix-P (N) 588 653Compression Recovery (%) 3.81 4.47 Max Compression (%) 13.82 15.20 FinalCompression (%) 10.01 10.73

FIG. 5 and Table 3 shows the compression profile for various porousmembranes. When compared to other 12 μm membranes the microlayerconstruction shows a balanced compression recovery profile, while it canbe compressed it does offer some recovery which may be critical incertain particular battery applications. In at selected embodiments, theinstant microlayer or nanolayer technology may be comprised of greaterthan 50 layers. These layers may be created in a pre-encapsulationfeedblock first before entering either a cast-film die or a blown filmdie. The microlayers may be created in the feedblock by layermultiplication (one example in FIG. 7) or layer splitting (one examplein FIG. 8). When used in making porous membrane precursors, thesetechniques may further improve strength and flex-crack resistance. Theseprecursors would be laminated, annealed, and stretched, and theresulting membrane may exhibit improved strength and toughness.Furthermore, by leveraging these techniques it may alleviate the need touse polymers with molecular weights greater than 1M whose processing canbe very difficult, especially in dry process membranes.

In other selected particular embodiments, microlayers may be used tocreate a modified trilayer membrane. In this embodiment, the microlayerswould comprise or consist of alternating polymers, and the resultingmembrane would be: PP/PE/PP/PE/PP/PE/PP/PE/PP. The precursor membranesmay be extruded with microlayers of PP/PE/PP and PE/PP/PE, thesemicrolayer precursors may subsequently be laminated together and thenstretched to achieve the desired porosity. The polypropylene may be anyhomopolymer PP, copolymer PP and/or polymer blends. The polyethyleneutilized may be High Density Polyethylene (HDPE) or any polyethylenewith comonomers, copolymers and/or polymer blends.

TABLE 4 Additional inventive examples: PP Pore PE Pore Surface ProductStretch Ply Size Size Porosity Area Number Lot # No. (μm) (μm) (%)(m²/g) R0367 C3306986 na 0.0354 na 39.59 88.29 C3306987 na 0.0369 na38.70 81.41 R0374 C3338198 2 0.0299 0.0646 37.66 86.76 C3338198 5 0.03060.0675 37.80 85.75 C3338199 2 0.0295 0.0643 36.83 84.73 C3338199 50.0302 0.0666 37.11 84.45 C3338200 2 0.0309 0.0692 38.19 85.31 C33382005 0.0303 0.0676 38.34 87.23 R0384 C3435497 2 0.0402 0.0533 39.98 76.84C3435497 5 0.0415 0.0552 40.18 74.33 C3435498 2 0.0390 0.0514 38.8074.65 C3435498 5 0.0399 0.0521 39.03 73.78 C3435499 2 0.0378 0.050738.93 76.37 C3435499 5 0.0376 0.0515 39.11 77.33

Also, certain inventive microlayer or nanolayer constructions may yieldgreater surface area.

The FIG. 1-3 cross-sectional SEMs may show columns, pillars, columnar,columnal, columned, or columnated substantially vertical crystallinepolymer structures. These columns or pillars of crystalline polymer mayenhance strength, improve DB, and/or the like.

In accordance with at least selected embodiments, aspects or objects,the present application or invention may address the above needs orissues and/or may provide novel or improved membrane layers, membranesor separator membranes, battery separators including such membranes,and/or related methods. In accordance with at least selectedembodiments, the disclosure or invention relates to novel or improvedporous membranes or separator membranes, battery separators includingsuch membranes, and/or related methods. In accordance with at leastcertain embodiments, the disclosure or invention relates to novel orimproved microporous membranes or separator membranes, microlayermembranes, multi-layer membranes including one or more microlayermembranes, battery separators including such membranes, and/or relatedmethods. In accordance with at least certain selected embodiments, thedisclosure or invention relates to novel, optimized or improvedmicroporous membranes or separator membranes having one or more novel orimproved exterior layers and/or interior layers, microlayer membranes,multi-layered microporous membranes or separator membranes havingexterior layers and interior layers, some of which layers are created byco-extrusion and all of which layers are laminated together to form thenovel, optimized or improved membranes or separator membranes. In someembodiments, certain layers comprise a homopolymer, a copolymer, and/ora polymer blend. The invention also relates to methods for making such amembrane, separator membrane, or separator, and/or methods for usingsuch a membrane, separator membrane or separator, for example as alithium battery separator. In accordance with at least selectedembodiments, the present application or invention is directed to novelor improved multi-layered and/or microlayer porous or microporousmembranes, separator membranes, separators, composites, electrochemicaldevices, batteries, methods of making such membranes, separators,composites, devices and/or batteries. In accordance with at leastcertain selected embodiments, the present invention is directed to anovel or improved separator membranes that are multi-layered, in whichone or more layers of the multi-layered structure is produced in amulti-layer or microlayer co-extrusion die with one or more extrudersfeeding the die (typically one extruder per layer or microlayer). Theimproved membranes, separator membranes, and/or separators maypreferably demonstrate improved shutdown, improved strength, improveddielectric breakdown strength, and/or reduced tendency to split.

The present disclosure or invention may relate to novel or improvedmembranes or separator membranes, battery separators including suchmembranes, and/or related methods. In accordance with at least selectedembodiments, the disclosure or invention relates to novel or improvedporous membranes or separator membranes, battery separators includingsuch membranes, and/or related methods. In accordance with at leastcertain embodiments, the disclosure or invention relates to novel orimproved microporous membranes or separator membranes, microlayermembranes, multi-layer membranes including one or more microlayermembranes, battery separators including such membranes, and/or relatedmethods. In accordance with at least certain selected embodiments, thedisclosure or invention relates to novel, optimized or improvedmicroporous membranes or separator membranes having one or more novel orimproved exterior layers and/or interior layers, microlayer membranes,multi-layered microporous membranes or separator membranes havingexterior layers and interior layers, some of which layers are created byco-extrusion and all of which layers are laminated together to form thenovel, optimized or improved membranes or separator membranes. In someembodiments, certain layers comprise a homopolymer, a copolymer, and/ora polymer blend. The invention also relates to methods for making such amembrane, separator membrane, or separator, and/or methods for usingsuch a membrane, separator membrane or separator, for example as alithium battery separator. In accordance with at least selectedembodiments, the present application or invention is directed to novelor improved multi-layered and/or microlayer porous or microporousmembranes, separator membranes, separators, composites, electrochemicaldevices, batteries, methods of making such membranes, separators,composites, devices and/or batteries. In accordance with at leastcertain selected embodiments, the present invention is directed to anovel or improved separator membranes that are multi-layered, in whichone or more layers of the multi-layered structure is produced in amulti-layer or microlayer co-extrusion die with multiple extruders. Theimproved membranes, separator membranes, or separators may preferablydemonstrate improved shutdown, improved strength, improved dielectricbreakdown strength, and/or reduced tendency to split.

In accordance with at least selected embodiments, a battery separator orseparator membrane comprises one or more co-extruded multi-microlayermembranes optionally laminated or adhered to another polymer membrane.The separators described herein may provide improved strength, forexample, improved puncture strength, particularly at a certainthickness, and may exhibit improved shutdown and/or a reduced propensityto split.

Test Methods

Gurley

Gurley is defined herein as the Japanese Industrial Standard (JISGurley) and is measured herein using the OHKEN permeability tester. JISGurley is defined as the time in seconds required for 100 cc of air topass through one square inch of film at a constant pressure of 4.9inches of water.ThicknessThickness is measured in micrometers, μm, using the Emveco Microgage210-A micrometer thickness tester and test procedure ASTM D374.Tensile StrengthMachine Direction (MD) and Transverse Direction (TD) tensile strengthare measured using Instron Model 4201 according to ASTM-882 procedure.Tensile Strength% MD elongation at break is the percentage of extension of a test samplealong the machine direction of the test sample measured at the maximumtensile strength needed to break a sample.% TD elongation at break is the percentage of extension of a test samplealong the transverse direction of the test sample measured at themaximum tensile strength needed to break a sample.Puncture StrengthPuncture Strength is measured using Instron Model 4442 based on ASTMD3763. The measurements are made across the width of the microporousmembrane and the puncture strength defined as the force required topuncture the test sample.Thermal ShrinkageShrinkage is measured by placing a test sample between two sheets ofpaper which is then clipped together to hold the sample between thepapers and suspended in an oven. For the ‘105° C. for 1 hour’ testing, asample is placed in an oven at 105° C. for 1 hour. After the designatedheating time in the oven, each sample was removed and taped to a flatcounter surface using double side sticky tape to flatten and smooth outthe sample for accurate length and width measurement. Shrinkage ismeasured in the both the Machine direction (MD) and Transverse direction(TD) direction and is expressed as a % MD shrinkage and % TD shrinkage.Pore SizePore size is measured using the Aquapore available through PorousMaterials, Inc. (PMI). Pore size is expressed in μm.PorosityThe porosity of a microporous film sample is measured using ASTM methodD-2873 and is defined as the percentage void spaces in a microporousmembrane measured in both Machine Direction (MD) and TransverseDirection (TD).Dielectric Breakdown (DB)Voltage is applied to a separator membrane until the dielectricbreakdown of the sample is observed. Strong separators show high DB. Anynon-uniformity in the separator membrane leads to lower DB values.Compression ElasticityCompression elasticity modulus was evaluated using the TMA Q400 and ahemi-sphere probe. A 5 mm×5 mm sample is compressed at a constant rateup to 1 N (568 N/cm2), then the pressure is released at a constant rateback down to 0 N at ambient temperature. Percentage of dimension changeduring compression and recovery are estimated based on the initialthickness of the sampleMixed PenetrationMixed Penetration is the force required to create a short through aseparator when placed between cathode and anode materials. This test isused to indicate the tendency of a separator to allow short circuitsduring the battery assembly. Details of this method are described in US2010/209758.Cycling

All cycling was done in constant current (CC) mode. Cathode used is 523NMC. Anode used is superior graphite. Electrolyte used 1 M LiPF₆ salt in3:7 v:v EC:EMC solvent. Voltage window is 3.0-4.3 V. Cycles 1-5 havecharge rate and discharge rate of C/10. Cycles 6-10 have a charge rateand discharge rate of C/5. Cycles 11-15 have a charge rate of C/5 and adischarge rate of C/2. Cycles 16-20 have a charge rate of C/5 and adischarge rate of 1 C (charge/discharge rate capacity; 1 C is a rate offull charge or discharge in 60 minutes). Cycles 21-25 have a charge rateof C/5 and a discharge rate of 5 C. Cycles 26-30 have a charge rate ofC/5 and a discharge rate of 10 C. Cycles 31-35 have a charge rate anddischarge rate of C/10.

We claim:
 1. A battery separator for a lithium battery comprising: atleast one dry-process microporous polymer membrane comprising aplurality of co-extruded porous polymer microlayers with a thickness ofless than 2 microns; and at least two other dry-process microporouspolymer membranes, wherein the at least one dry-process microporouspolymer membrane comprising a plurality of co-extruded porous polymermicrolayers with a thickness of less than 2 microns and the at least twoother dry process microporous polymer membranes are laminated to oneanother.
 2. The battery separator of claim 1 wherein the at least twoother dry-process microporous polymer membranes comprise at least oneselected from a monolayer dry-process microporous polymer membrane andanother dry-process microporous polymer membrane comprising a pluralityof porous polymer microlayers having a thickness of less than 2 microns.3. The battery separator of claim 2, wherein at least three microporousdry-process polymer membranes of co-extruded polymer microlayers with athickness of less than 2 microns are laminated together to form thebattery separator.
 4. The battery separator of claim 3, wherein the atleast three said microporous dry-process polymer membranes ofco-extruded polymer microlayers with a thickness less than 2 micronseach comprise at least three polymer microlayers.
 5. The batteryseparator of claim 1 wherein said at least one microporous polymerdry-process membrane comprising a plurality of co-extruded porouspolymer microlayers with a thickness of less than 2 microns has at leastthree microlayers with a thickness of less than 2 microns.
 6. Thebattery separator of claim 1 wherein at least one of said microporousdry-process polymer membranes of co-extruded polymer microlayers of lessthan 2 microns is made of one or more polyolefins.
 7. The batteryseparator of claim 1 wherein at least one of said microporousdry-process polymer membranes of co-extruded polymer microlayers is madeup of coextruded dry-process polyolefin microlayers with a thickness ofless than 2 microns.
 8. A lithium battery comprising the batteryseparator of claim
 1. 9. A secondary lithium battery comprising thebattery separator of claim
 1. 10. A battery separator comprising one ormore dry-process microporous polymer co-extrudedmulti-microlayer-membranes with the microlayers having a thickness ofless than 2 microns, wherein the one or more dry-process microporouspolymer co-extruded multi-microlayer membranes with microlayers having athickness of less than 2 microns are laminated to at least two otherdry-process polymer membranes, which may be a dry-process microporouspolymer co-extruded multi-microlayer-membranes with microlayers having athickness of less than 2 microns, and wherein the battery separatorprovides at least one of the following: improved strength in comparisonto a conventional trilayer membrane, improved shutdown in comparison toa conventional trilayer membrane, and a reduced propensity to split incomparison to a conventional trilayer membrane.
 11. A lithium batterycomprising the battery separator of claim
 10. 12. A separator membranecomprises one or more dry-process co-extruded multi-microlayer polymermembranes laminated to at least two other dry-process polymer membranes,which may be another dry-process co-extruded multi-microlayer polymermembrane, wherein the separator membrane exhibits at least one of thefollowing: improved strength in comparison to a conventional trilayermembrane, improved puncture strength in comparison to a conventionaltrilayer membrane, improved shutdown in comparison to a conventionaltrilayer membrane, and a reduced propensity to split in comparison to aconventional trilayer membrane.
 13. A lithium battery comprising theseparator membrane of claim 12.